Engine exhaust systems utilize hydrocarbon retaining devices, such as hydrocarbon (HC) traps, to retain cold start emissions (HC storing) for later reaction, or to recirculate (HC purging) into the engine intake system. However, in engines such as gasoline-based direct-injection engines, when operating at high loads, a substantial amount of fine particulate matter (such as soot) may also be generated. The particulate matter (PM) may not be effectively removed by such hydrocarbon traps. When released into the atmosphere, these fine particles can pose serious environmental and health risks.
Some of the above issues may be addressed by a method of operating an engine including an exhaust treatment system coupled to an engine exhaust, the exhaust treatment system further coupled to an engine intake via an exhaust gas recirculation (EGR) system. In one embodiment, the method comprises, operating in a first mode including routing exhaust gas through the exhaust treatment system to an exhaust tailpipe; operating in a second mode including routing exhaust gas through the exhaust treatment system to an engine intake via the EGR system, and operating in a third mode including routing exhaust gas to an engine intake through the EGR system while bypassing the exhaust treatment system.
In one example, during an engine cold start condition, exhaust gas may be routed through the exhaust treatment system to an exhaust tailpipe to store exhaust hydrocarbons (HCs) and particulate matter (PM) in the exhaust treatment system. In another example, during a purging condition, exhaust gas may be routed through the exhaust treatment system to an engine intake via an EGR system, such as a low pressure EGR system, to purge the stored HCs and PMs to the engine intake. In yet another example, during an EGR condition, exhaust gas may be routed to the engine intake through the EGR system while bypassing the exhaust treatment system to only recirculate exhaust gas to the engine intake. In this way, an exhaust treatment system may be used to store exhaust HCs and PMs until a catalyst light-off temperature is reached, following which the purge flow of stored HCs and PMs may also be used an EGR flow. Further, when desired, an EGR operation independent of the exhaust treatment system may also be performed.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.